This invention relates to a rectangular electric contact for use in a switch.
Although most switch contacts are circular, it is also quite common to employ angularly shaped contacts (particularly rectangularly shaped ones) in order to assure reliable contact even if some degree of misalignment should occur between contact pairs.
Circular contacts have heretofore been manufactured by two methods: One method involves fabricating rivet-shaped contact pieces out of a contact stock such as of silver, copper or alloys thereof, inserting the rivet-shaped contact pieces into holes made in or through base pieces such as of copper or brass and fastening the contact pieces firmly onto the base pieces as by hammering or pressing; and, the other method comprises welding circular contact pieces onto base pieces.
In the case of rectangular contacts, however, rivet-shaped rectangular contact pieces are difficult to mass produce because of the complex shape of the contact. Thus, it has been an established practice to form such rectangular contacts by welding rectangular contact pieces onto corresponding base pieces.
Contacts produced by resistance welding, however, have several problems. Since both the contact pieces and the base pieces are inherently made of substances of low electric resistance, the two pieces are welded by the projection welding technique. In welding by this method, since fusion between the pieces occurs only in the region of projection where the electric current is concentrated, the area of fusion between the two pieces is only about 5 to 10% of the total area of apparent contact. The area of such apparent contact between the two pieces, therefore, has substantially no electrical or thermal conductivity and the area of fast fusion has limited conductivity. Thus, these contacts do not fully satisfy their function. To make matters worse, these contacts do not readily permit thorough inspection of the welded portions. If a contact with imperfect fusion between the contact piece and the base piece should escape detection in the inspection, there is a fair possibility of the contact piece coming off the base piece while the contact is in service. Contacts made by resistance welding are thus unreliable. A further problem issues from the inevitable intervention of a projection between the contact piece and the base piece while the welding work is in process.
Consequently, it is difficult to secure accurate control of the position at which the contact piece is welded onto the base piece. It is also difficult to manufacture all the contact pieces in a uniform height. Thus, there is a possibility that the opposed contacts in some of the assembled switches will fail to come into effective contact or that the position at which the switching is effected will vary from one switch to another. Particularly in the case of micro-switches which are required to offer dimensional accuracy on the order of microns as to the contacts incorporated therein, the variation in quality in the individual switches being manufactured makes it impossible to obtain switches of accurate and reliable performance.
In spite of these unsolved problems, the aforementioned resistance welding technique continues to be used for the sole reason that there exists no other effective mass-production technique.
The inventor formerly developed a novel method for pressing a contact into position in the manufacture of micro-switches. This previously proposed method aims to accomplish mass production of contacts by feeding a metal strip as the stock for base pieces and a metal wire as the stock for contact pieces simultaneously into a continuous press and thereby attaching contact pieces to the corresponding base pieces by pressing and, at the same time, forming the individual base pieces as combined firmly with the contact pieces in a required shape to give rise to micro-switches (U.S. Pat. No. 3,967,369).